The present invention relates to a driving method of a ceramic heating element which is used as a heating element for an infrared ray source.
FIG. 4 shows an example of a ceramic heating element, generally indicated by the numeral 1, as an infrared ray source.
A heating element 1 is constructed of a sheet member with a thickness of about 0.5 mm, which is formed by shaping a raw material powder into a sheet and burning or sintering the same. The sheet member is processed by an electrical discharge method to form a zigzag heating element 11 and linear lead members 12a, 12b and is attached to a ceramic tube 14 by heat-resistant adhesive material 13. Incidentally, 2a and 2b designate lead wires which are connected to the lead members 12a and 12b, respectively.
The ceramic heating element 1 as an infrared ray source shown in FIG. 4 is normally driven by a direct-current (DC) voltage so as not to cause unsteadiness or instability in the quantity of light. However, when a temperature at the heating element is around 1,500 .degree. C. and heating time becomes several hundred hours, a temperature distribution of the heating element may change locally or deformation might occur, ultimately resulting in disconnection.
Also, it is confirmed that this kind of abnormality remarkably occurs on the positive terminal side. It is presumed that this is not because of unevenness or heterogeneity of the material, but because of migration of atoms.
Therefore, an object of the invention is to prevent abnormality such as deformation being caused in the ceramic heating element as the infrared ray source, and to improve the reliability of the heating element.
Further objects and advantages of the invention will be apparent from the following description of the invention.